Face-centered Cubic Packing Research Articles

Cold energy storage in a packed bed with novel structured PCM capsule layouts

Based on the closest packing principle of the crystal structure, three configurations of the spheres in cylindrical packed beds are presented in this study: aligned density layer (ADL), face-centered cubic (FCC), and hexagonal closest packed (HCP). Both numerical simulations and experimental tests are conducted to study the flow and heat transfer characteristics of these packing patterns with Reynolds numbers ranging from 1 to 200. The results show that at a constant flow rate of 100 L/h, the charge durations of FCC and HCP packing are shorter by 27.8 % and 20.8 %, respectively, than those of ADL packing. Additionally, the potential PCM packing density for FCC and HCP layouts is increased by 42.3 %, which significantly reduces the packed bed's footprint. Considering both heat transfer and pressure drop, the FCC packing layout achieves the highest overall evaluation factor of 1.19, followed by HCP and ADL packing. Finally, a self-defined normalized charging efficiency factor of βcharge which considers the cooling capacity storage at the cost of pump hydraulic power is proposed, and the value of βcharge for FCC is the best (34.7 % higher than that of ADL), followed by HCP (22.8 % higher than that of ADL).

Determination of the effect of the open cell foam material geometry on the value of energy efficiency

THE PURPOSE. Improving the energy efficiency of open cell foam materials with different geometries (SC, BCC, FCC, DEM) and with different medium porosities (ε=0.7; ε=0.75; ε=0.8; ε=0.85; ε=0.9; ε=0.95) by numerical simulation. To determine the influence of the geometry and porosity of an open cell foam material on the values of pressure drop, heat flux and energy efficiency factor.METHODS .Numerical simulation was carried out using the ANSYS Fluent 19.2 software package. Geometric models of porous structures are sets of intersecting spheres with different packing structures: periodic Simple Cubic packing (SC), Face Centered Cubic packing (FCC), Body Centered Cubic packing (BCC), and random structure generated by the discrete element method (DEM).The calculations were carried out at the following air flow velocities: 0.01; 0.05; 0.25; 0.5; 0.75; 1; 1.25 m/s.RESULTS. Atair flow velocities of 0.01 m/s and 0.05 m/s, all the studied structures show approximately the same heat flux. With porosity values ε=0.75; ε=0.8; ε=0.85 the highest values of heat flow were shown by the FCC structure, with porosity ε=0.7; ε=0.9; ε=0.95 the BCC structure had the highest heat flux. This is explained by the fact that, at the corresponding porosity values, the FCC or BCC structure had the largest surface area, which provided the largest heat flux. With the porosities of media ε=0.7 and ε=0.75, the BCC and FCC cell packages show a high pressure drop. With the porosities of media ε=0.8 and ε=0.85, the highest pressure drop corresponds to FCC cell packing, and for porosities ε=0.9 and ε=0.95, to BCC cell packing.CONCLUSION. With equal high porosity, the BCC cell packing provides a higher value of heat flux than the FCC structure. The SC package has the lowest heat flux values for all studied porosities. The SC package also has the lowest pressure drop values and therefore the highest energy efficiency values.

Assessment of flow pattern and temperature profiles by residence time distribution in typical structured packed beds

The flow and temperature fields in packed beds are rather complex but are of great importance since they will influence macroscopic parameters and the overall performance of the packed bed system. Regions with either too high or too low velocity are not preferred since they will decrease the heat and mass transfer characteristics of packed beds. The residence time distribution (RTD) is a way to assess the characteristics of the flow maldistribution, where a narrower distribution is closer to the ideal plug flow with less dispersion. In this article, the RTD in three typical structured packed beds, namely, the simple cubic (SC) packing, the body-centered cubic (BCC) packing and the face-centered cubic (FCC) packing, are studied by using ANSYS FLUENT. Results show that, firstly, the RTD curve can be used to diagnose the flow pattern in packed beds where the skewed peak indicates the channeling effect and a long tail relates to recirculation. It is revealed secondly that, FCC packing has the narrowest RTD curve in the studied structures, BCC packing comes second and SC packing has the flattest RTD curve, which demonstrates that the flow uniformity in FCC packing is the best. For the same packing form, the flow is less maldistributed at higher velocity. Finally, it is shown that the packing form with less dispersion, which behaves more like the ideal plug flow, has a more uniform distribution of the particle-to-fluid heat transfer coefficient near the particle surface.

Rectangular Body-centered Cuboid Packing Lattices and Their Possible Applications

We first introduce several sphere packing ways such as simple cubic packing (SC), face-centered cubic packing (FCC), body-centered cubic packing (BCC), and rectangular body-centered cuboid packing (recBCC), where the rectangular body-centered cuboid packing means the packing method based on a rectangular cuboid whose base is square and whose height is times the length of one side of its square base such that the congruent spheres are centered at the 8 vertices and the centroid of the cuboid. The corresponding lattices are denoted as SCL, FCCL, BCCL, and recBCCL, respectively. Then we consider properties of those lattices, and show that FCCL and recBCCL are the same. Finally we point out some possible applications of the recBCC lattices.

Atomic packing controls exciton lifetime

Nanomaterials Like semiconductors, small metallic clusters can absorb light and create excitons (electron-hole pairs). In ligand-capped gold clusters of 30 to 40 atoms (Au30 to Au40) that adopt the usual face-centered cubic packing, the lifetime of these excitons is ∼100 nanoseconds. Zhou et al. found that atomic packing and molecular orbital overlap can greatly affect carrier lifetimes. Despite having similar bandgaps to those of face-centered cubic clusters, a hexagonal close-packed Au30 cluster had a much shorter lifetime (∼1 nanosecond), and a body-centered cubic Au38 cluster had a lifetime of ∼5 microseconds, which is comparable to bulk silicon. Science , this issue p. [279][1] [1]: /lookup/doi/10.1126/science.aaw8007

Particle filtration characteristics of typical packing granular filters used in hot gas clean-up

Granular filter is a promising method in hot gas clean-up for advanced coal gasification technologies. Numerical simulations were performed in this paper for the particle filtration characteristics of granular filters with two typical packings: body centered cubic (BCC) and face centered cubic (FCC) packings. Fluid flow characteristics were investigated and pressure drop correlations for the two granular packings were obtained. The pressure drop of both packings increases linearly with the increase of velocity, and the pressure drop of the FCC packing is significantly higher than that of BCC. The discrete phase model (DPM) was employed to trace fly ash particle motion during the filtration process, and particle deposition characteristics on the granular surface, including the particle penetration, deposition distribution of different particle sizes, and deposition distribution along filter layers were determined. The deposition fraction of particles on each layer of granules decreases with the increase of row number, and the maximum deposition location is different for BCC and FCC packings. Large particles mainly deposit on the first four layers of granules, while small particles deposit over all layers. The collection efficiency of BCC and FCC packings increases with the increase of velocity, and they decrease first and then increase with particle diameter. Correlations of collection efficiency for the two granular packings are presented and they have good prediction accuracy.

Three-Dimensional Cyclic Voltammetry Simulations of EDLC Electrodes Made of Ordered Carbon Spheres

This study aims to investigate the effect of electrode nanoarchitecture on the performance of electric double layer capacitor (EDLC) porous electrodes consisting of highly-ordered monodisperse spherical carbon nanoparticles. To do so, cyclic voltammograms, reproducing three-electrode measurements, were numerically generated for electrodes with different thicknesses and nanoparticle diameters arranged in either simple cubic (SC) or face-centered cubic (FCC) packing structure. The transient three-dimensional simulations of interfacial and transport phenomena in the porous electrodes were based on a continuum model accounting for (1) binary symmetric electrolytes with finite ion size, (2) electric field-dependent dielectric constant of the electrolyte, (3) the Stern layer at the electrode/electrolyte interface, along with (4) Ohmic potential drop in the electrode. For both FCC and SC packing structures, the areal capacitance (in μF/cm2) increased with decreasing sphere diameter. In addition, for a given sphere diameter, FCC packing featured larger equilibrium capacitance than SC packing. These observations were attributed to larger electric field at the carbon sphere surface for smaller spheres and/or FCC packing. In all cases, the areal capacitance remained constant at low scan rates but decreased beyond a critical scan rate. The latter rate-dependent regime was reached at lower scan rates for thicker electrodes due to resistive losses across the electrode. Interestingly, limitation due to ion diffusion through the porous electrode was not observed. Finally, dimensional analysis was performed by scaling the CV cycle period by the time scale for electron transport in the electrode. This study illustrates powerful numerical simulation tools that can be used to select materials and electrolytes and to design and optimize EDLC electrodes.

Transport Phenomena in Electrical Double Layer Capacitors with Highly Ordered 3D Porous Carbon Electrodes

Electric double layer capacitors (EDLCs) store energy via ion adsorption in the electric double layer forming at the electrode/electrolyte interfaces in highly porous carbon electrodes. This charge storage mechanism is very fast and highly reversible resulting in large power density and long cycle life. Applications range from regenerative breaking for hybrid electric vehicles to the smart grid. The architecture of the carbon electrodes is known to have a significant effect on the performance of EDLCs. Unfortunately, experimental optimization can be time consuming and challenging due to the large number of design parameters. Numerical simulations could offer a faster and less costly alternative. This study aims to demonstrate the use of numerical tools to simulate transient three-dimensional interfacial and transport phenomena in EDLCs with realistic electrode architecture. It also aims to derive design rules for EDLC porous electrodes. To do so, cyclic voltammograms were numerically generated for EDLCs consisting of electrodes with highly-ordered spherical carbon nanoparticles arranged in simple cubic (SC) or face-centered cubic (FCC) packing in LiClO4/propylene carbonate electrolyte. Simulations were performed for different carbon nanoparticles diameter, electrode thickness, and scan rate. The continuum model was based on the modified Poisson-Nernst-Planck model and accounted for (i) the Stern layer at the electrode/electrolyte interface, (ii) finite ion size, (iii) binary and symmetric electrolyte, and (iv) three-dimensional electrode morphologies. In all cases, the areal capacitance was independent of scan rate at low scan rate but decreased beyond a critical scan rate corresponding to the diffusion-limited regime when ion transport cannot follow the rapid changes in electric potential. The results indicate that the areal capacitance (in F/m2) increased with decreasing sphere diameter below 40 nm due to the increasing surface curvature resulting in larger surface electric field. In addition, FCC packing featured larger capacitance that SC packing thanks to larger surface electric field for given sphere diameter and low scan rate . However, the ion diffusion regime was reached at lower scan rates in FCC packing because of the higher turtuosity limiting the ion transport in the electrode.

Effective elastic moduli of core-shell-matrix composites

The effective Young’s modulus and Poisson’s ratio of spherical monodisperse and polydisperse core-shell particles ordered or randomly distributed in a continuous matrix were predicted using detailed three-dimensional numerical simulations of elastic deformation. The effective elastic moduli of body-centered cubic (BCC) and face-centered cubic (FCC) packing arrangements of monodisperse microcapsules and those of randomly distributed monodisperse or polydisperse microcapsules were identical. The numerical results were also compared with predictions of various effective medium approximations (EMAs) proposed in the literature. The upper bound of the EMA developed by Qiu and Weng (1991) was in good agreement with the numerically predicted effective Young’s modulus for BCC and FCC packings and for randomly distributed microcapsules. The EMA developed by Hobbs (1971) could also be used to estimate the effective Young’s modulus when the shell Young’s modulus was similar to that of the matrix. The EMA developed by Garboczi and Berryman (2001) could predict the effective Poisson’s ratio, as well as the effective Young’s modulus when the Young’s modulus of the core was smaller than that of the matrix. These results can find applications in the design of self-healing polymers, composite concrete, and building materials with microencapsulated phase change materials, for example.

Simulation of electric double layer capacitors with mesoporous electrodes: Effects of morphology and electrolyte permittivity

Abstract This paper aims to numerically predict the capacitance of electric double layer capacitors (EDLCs) made of mesoporous electrodes consisting of closely packed monodispersed mesoporous carbon spheres in (C 2H 5) 4NBF 4/propylene carbonate electrolyte. The model faithfully accounts for the electrode packing morphology and the dependency of electrolyte dielectric permittivity on local electric field. Three sphere packing morphologies were investigated, namely, simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC). A cylindrical mesopore in a mesoporous carbon sphere was also simulated. This study demonstrates that the field-dependent electrolyte dielectric permittivity significantly affects the predicted capacitance of EDLCs. Moreover, the Stern layer needs to be accounted for in order to match predicted specific area capacitance with experimental data. This study also establishes that, for all packing structures, larger sphere diameter results in larger electric field at the electrode surface and thus larger diffuse layer specific area capacitance. For sphere diameter less than 40 nm, SC packing had the largest electrolyte volume fraction. This provided more space for the electric potential to decrease resulting in larger electric field at the electrode surface and diffuse layer specific area capacitance compared with BCC and FCC packings. On the contrary, FCC features the smallest volume fraction resulting in the lowest surface electric field and diffuse layer specific area capacitance. The packing morphologies of electrode spheres were found to have no significant effect on the diffuse layer specific area capacitance for sphere diameter larger than 40 nm.

Mechanics of BCC and FCC hollow-sphere foams

Hollow-sphere foams provide an alternative microstructure for low-density metal structures with the potential for improved properties. In a recent companion paper, the mechanical properties of hollow-sphere foams with simple cubic packing (SC) were shown to be close to the theoretical values for closed-cell foams and well above the measured modulus and strength of metallic closed-cell foams. Here, we analyze the elastic moduli and initial yield strength of body-centered cubic and face-centered cubic (FCC) packings of hollow-sphere foams. In general, the FCC packing gives the highest values of moduli and strengths.